Firstly, I want to apologise for not posting last week. I flew back cross country to come back home on Tuesday morning last week and so did not get much accomplished on that day. I then spent a few days recovering, and only really started getting my act together on the weekend. That said, be prepared, for this is a reasonably long one … no pun intended with the story I will be telling.

All that said, today, we will be continuing to Think Like a Medical Student by looking at Retroperitoneal Schwannoma: A Case Report ((Garcia Blanco CE, Roblesa Cruz MM, Quezada Fiallos CM. Retroperitoneal Schwannoma: A Case Report. Internal Medicine: Open Access 2018;08(05).)). This article was recently published by Garcia Blanco CE, Roblesa Cruz MM, and Quezada Fiallos CM, in Internal Medicine: Open Access, volume 8, issue 5, in January 2018, and with a DOI of 10.4172/2165-8048.1000292. But, first, a story from my own life experience.

Over the Christmas period, I was visiting my family back home. It was an enjoyable time, and I caught up with basically everyone I wanted to. However, living back with other people made some slight changes to my normal living arrangements by myself in a studio apartment.

One night, it might have been Christmas Eve, I woke up at around 03:30. I was absolutely busting to go to the toilet (to urinate). However, I was also tumescent. The word tumescent is derived from the Latin word tumere, which means “to swell”, and is the same word we get tumour from (which also means “a swelling”). So, in more normal language, I had an erection. Back when I was younger, I used to think that needing to pee really badly could cause an erection. However, I had since learnt that that was wrong, and I had also learnt (during my erectile dysfunction presentation in my undergraduate program) that nocturnal erections were a normal occurrence for males (of all ages).

As such, I had made the assumption that what people think is an erection from needing to pee was just a nocturnal erection correlated and misattributed. So, I waited for it to subside. However, after some time, over five minutes, it still hadn’t resolved. I decided that I couldn’t wait anymore. Besides, due to the time, nobody else would be up then. So, I went to the toilet and voided my bladder. Incidentally, I noted that the erection was also completely resolved upon relieving myself. Questioning this, and being certain that the erection was caused by the need to urinate, I investigated at four in the morning.

Why does needing to pee cause an erection?

I was already aware that the logical assumption was wrong. Specifically, the “logical assumption” would be that the penis is filled with urine, causing a pseudo erect state. However, I knew two things. Firstly, I knew that the external urethral sphincter, the muscles that hold the urine inside the body, is positioned at the distal prostate (i.e., the end of the prostate furthest from the bladder). This is well inside what we’ll call the body, i.e., before the penis begins. In fact, females also have this sphincter, in roughly the same anatomical position (sans the prostate obviously), showing that it has to be before the penis starts. Secondly, I knew that the sensation I had was the full erect (rigid) state and not just the tumescent (swollen) state.

The default state for the penis is termed the flaccid state, meaning the soft state where no arousal is occurring. The tumescent state is the first stage of sexual arousal and is caused by dilation of the blood vessels of the penile tissue, specifically of the corpus cavernosum tissues. The penis contains two of these, which fill with blood to form the erect penis, and one corpus spongiosum, through with the urethra passes allowing urine (and sperm during ejaculation) to flow. The erect (rigid) state is the next stage when the blood within the corpus cavernosum compresses the veins. This prevents (some) blood from leaving the penile tissues, which results in the penis becoming filled and rigid.

All that said, I was not sexually aroused during the whole preceding process. I needed to figure this out. After a bit of investigating, I started to query whether the sufficiently full bladder pressed on the prostate and if this had an arousing effect. This wound up being a dead end directly, and I hadn’t really thought it was the case anyway. It did, however, lead me to a paper named Physiology of Penile Erection and Pathophysiology of Erectile Dysfunction ((Dean RC, Lue TF. Physiology of penile erection and pathophysiology of erectile dysfunction. The Urologic clinics of North America 2005;32(4):379-v.)). This paper helped me formulate an answer that I think is possibly what was occurring. It also would have been very handy to have found back when I did my paper on this very topic, although I likely wouldn’t have understood it at the time.

Running directly adjacent to the prostate on either side are what are known as the cavernous nerves. These nerves and their various branches run so close to the prostate, bladder, sphincters and rectum that they are frequently damaged during surgery to remove these structures, a common cause of surgically acquired erectile dysfunction
((Dean RC, Lue TF. Physiology of penile erection and pathophysiology of erectile dysfunction. The Urologic clinics of North America 2005;32(4):379-v.)). As such, my theory is that compression of these nerves by the bladder, or the prostate being pressed against them by the bladder, is the cause of an erection from being at maximal urine capacity. This would be similar to how compression of the median nerve in carpal tunnel syndrome causes paraesthesia (burning or prickling sensation) and pain in the hands. Cauda equina syndrome is another example, where compression of (mainly) sacral nerves (commonly from a herniated disc) causes pain and numbness across the lower back and leg. These all seem to be false signals being generated due to compression.

All that is just to say that nerves are fascinating, can be relatively easily impacted and have varying presentations. A full discussion of even nerves and just the peripheral nervous system would take much longer than we have available, as this topic alone consumed a fortnight of medical school study. Finally, on to the case!


The history presented for this article is reasonably simple. A 24-year-old male presents with abdominal pain and right lower limb (RLL) paraesthesia (reminder from two paragraphs ago: burning and prickling sensation). He also has a mass in the right side of the abdomen, which all things considered is likely related. This was stable with gradual progression over three years and was otherwise asymptomatic (did not produce any other symptoms).

Immediately, possible diagnoses and important questions are generated. Where specifically is the abdominal pain? What is the nature of the pain (burning, crushing, stabbing, etc.)? A major question is whether the pain is intermittent and/or associated with eating, as this can help to identify if the issue is related to the intestinal tract or gallbladder? Etc. Furthermore, what is the distribution of the RLL sensations? This sensation is most commonly caused by nerve involvement, and this information allows consideration of potential causes. More specifically, it allows consideration of which nerves are likely to be involved. Finally, due to the three-year course, have any investigations been performed previously, most likely (given an unexplained mass) including some form of imaging?

When the case progressed to the point of being investigated further (in February 2015) the patient was describing right sided dull pain (rating this a five out of ten) with no radiation (i.e., it was only in one place and did not occur elsewhere), and was associated with paraesthesia of the RLL. Interestingly, this last point was not a new finding and seems odd to have been repeated in this case. I believe it is likely that they were indicating that it was still associated with this and this emphasis was lost in translation.

The slow progression, and lack of other medical history (such as weight loss, muscle wasting, constitutional symptoms, etc.), are reasonably good signs for this case. One of the significant differentials that had to be considered in my opinion was some form of cancerous process. These signs seem to indicate a non-malignant process at work.


The examination showed a patient in good general condition with normal vital signs. This again helps to indicate a non-malignant process and also indicates away from various other conditions such as infection. Furthermore, this helps to exclude issues such as cirrhosis (significant liver failure) which would produce jaundice (yellowing of the skin), acute pancreatitis (which can be extremely painful) and cholelithiasis (gallstones, which can produce biliary colic, an intermittent extreme pain).

More specifically, the patient had a non-tender solid mass in the right hemiabdomen (i.e., the right half of the tummy). Tender, in medical parlance, means that pain occurs upon palpation (touching/pressing on the location). A non-tender mass implies either a chronic process (something taking a long time) or something that does not produce pain sensation (due to lack of neural innervation for that).

This mass is described as adhering to the deep plane (meaning that it is not in the superficial layers such as the skin and anterior muscles). It is also listed as being dull to percussion. As discussed previously, one step of examining tissues including a mass is to tap on the location using one finger pressed hard against the surface (known as a pleximeter) and the other tapping against that finger (known as the plexor). This process is similar to tapping on a wall to find concealed studs or hollow spaces. Another example would be like tapping on the skin of a drum. Based on the sound that is produced, the characteristics of the mass can be understood. For example, in the pleural space (i.e., the lungs), increased resonance to percussion indicates increased air underneath the pleximeter, whereas decreased resonance indicates increased mass or fluid in the area. In this particular instance, the dullness to percussion indicates that this mass is relatively solid without being filled with air.

Finally, the peripheral pulses of the legs are examined to assess the arteries and perfusion to the legs. These include the femoral pulses (near the groin area), the popliteal pulse (behind the knee), the posterior tibial pulse (the inside of the ankle), and the dorsalis pedis pulse (top of the foot near the base of the big toe). Additionally, capillary refill time was assessed by pressing down (most likely on a toenail) and seeing how quickly blood re-enters the space, with under two seconds being normal (as in this case). The comment on sensitivity and motor skills being normal indicates that musculoskeletal and neurological assessment was performed without any observed abnormality. These findings being normal helps to indicate that no cardiovascular involvement has occurred so far upstream from these locations.


Garcia Blanco CE, Roblesa Cruz MM, Quezada Fiallos CM. Retroperitoneal Schwannoma: A Case Report. Internal Medicine: Open Access 2018;08(05).

At last, the “meat” of the case. So far, we know that some sort of mass exists in the right abdomen, although it’s not particularly clear where exactly this is or what it could represent. There are numerous similar conditions that could present with a similar picture. So, we perform investigations to help out and narrow down the differentials to adjust our management.

Ultrasound and CT both showed a retroperitoneal tumour around L4 measuring 8 x 7 c.m. This mass displaced the ureter and the vessels on the same side. This is a reasonably dense sentence, so I will break it down a little.

Ultrasound is a non-radiation imaging technique which sends sound waves through your body and generates a picture from the bounces back (based on the echo, similar to a bats sonar). It is relatively low cost and impact, so is frequently used depending on the likelihood of it providing results. It is, however, quite operator dependent (i.e., the sonographer is heavily involved in the usefulness of the images). The CT scan (or CAT scan in the USA) stands for Computer Tomography (or Computer-Assisted Tomography), which is an image generated effectively by taking hundreds of X-ray’s from every direction will spinning around the patient in a helical pattern, then constructing a 3D model from this imaging. It is a considerably higher radiation dose than getting just a single X-ray (as it is just an X-ray but many times over), however, it is also strong for both localisation and visualising masses and lesions. If an X-ray by itself would be enough, it should be done, such as to investigate pneumonia. However, an unknown mass will normally require a CT.

Beyond CT are the more expensive, time-intensive and patient impacting modalities of the MRI and Nuclear Medicine imaging (and Positron Emission Tomography). These studies will rarely be done in the first instance but can be incredibly valuable in differentiating features on the grounds of anatomy/structure (MRI) or physiology/function (nuclear medicine/PET).

The ureter (urine duct from the kidneys to the bladder) and vessel (arteries and veins) displacement implies that further progression could potentially impact these structures. These could have various consequences. However, the simplest would be obstruction of the ureter could result in a buildup of urine back to the kidneys which could cause irreversible damage to the kidneys (among other complications) in a process known as hydronephrosis.

The mass is listed as being retroperitoneal. The peritoneum is basically a sack within the abdomen that contains most of the gastrointestinal organs, those organs involved in digestion and absorption of foods and liquids. The space behind this, but still within the abdominal cavity, is known as the retroperitoneal space. The retroperitoneal space includes numerous structures, memorable using the mnemonic SAID PUCKER (I don’t know, for some reason it sticks eventually): Suprarenal (adrenal) glands, Aorta and IVC (Inferior Vena Cava), Duodenum (parts 2 through 4), Pancreas, Ureters, Colon (ascending and descending), Kidneys, Esophagus, Rectum (at least partially). Of these, the ureters and branches of the Aorta and IVC (the abdominal supply vessels) are listed as being affected.

A tumour was reported. As indicated by my opening story for this post, tumour basically just means swelling, although most non-medical people will (incorrectly) think that “tumour” means cancer. Generally, “tumour” is used to refer to a mass that should not be in that location (or stretching outwards from an organ). Most simply, they are often neoplasms. Neoplasia literally means new growth and indicates the growth of cells that should not be occurring normally. Neoplasia can be broadly divided into two types: benign and malignant. Malignant neoplasia is generally what is meant when the word cancer is used. Benign neoplasms generally have no risk of metastasis or invasion into other tissues, however, they can cause problems most commonly from impacting on nearby structures (such as the ureters, vessels, and nerves supplying the legs).

Finally, the mention of “the level of L4” was made. Areas within the trunk, particularly those towards the back, can be described in regards to the corresponding spine bones in the area. The spine is composed of the cervical (head (below skull) and neck), thoracic (chest), lumbar (abdominal), sacral (pelvis), and coccygeal (tailbone) regions. Each has a varying number of vertebrae (although these are fairly constant between individuals), numbered from 1 superiorly (towards the crown of the head) and increasing downwards. L4 is referring to the 4th Lumbar vertebrae, which is at the level of the iliac crest (the bony parts at the top of your hips on the sides and back).

Stating the spinal level is helpful for two significant reasons. Firstly, it helps to localise where we are talking about and helps with future examination and investigation. Secondly, it allows consideration of what other structures could be affected at these levels. The nerves that receive branches from the L4 roots include the tibial nerve (back of the leg), fibular nerve (front of the leg), sciatic nerve (back of the thigh), femoral nerve (front of the thigh), and the superior gluteal nerve (primarily involved in keeping the hip steady during walking). As such, muscles and skin in these locations can be affected, with the skin distribution most likely matching what is known as the L4 dermatome. A dermatome is a region of skin that is innervated by a specific nerve root and is most useful in determining nerve damage or involvement.

Garcia Blanco CE, Roblesa Cruz MM, Quezada Fiallos CM. Retroperitoneal Schwannoma: A Case Report. Internal Medicine: Open Access 2018;08(05).

Finally, an MRI was performed, which allowed for the more clear establishment of the tumour’s boundaries and how it has affected surrounding structures. Blood tests were also obtained, which showed normal results. Altogether, the clinical picture, blood results, and imaging results indicate a benign tumour impacting on surrounding structures. Exploratory surgery was scheduled and a biopsy was performed, confirming a schwannoma, and another surgery was performed for removal of the mass.

A schwannoma is a benign tumour derived from Schwann cells. Schwann cells are cells of the body that coat nerves within the peripheral nervous system, providing both protection and allowing for faster transmission of nerve impulses. They are similar to the plastic coating around an electrical or fibre optic cable. As stated in the article, a schwannoma in this location is rare, however, they can theoretically occur anywhere that a nerve exists (i.e., anywhere in the peripheral nervous system) with a myelin sheath (a coating around the nerve). Most commonly they occur in the limbs or the cranial nerves (basically, the nerves of the head and throat), such as cranial nerve VIII, the vestibulocochlear nerve (involved in balance and hearing).


Well, this has been a long enough discussion, although the first third was my story. I hope you have enjoyed reading through it, and I know I didn’t cover numerous areas in enough detail. If you are interested about anything I raised in this post, feel free to put a comment down below and I can discuss it further.

The next post on Friday will be a much easier post to read I expect, and will be on how patient notes are written. I look forward to talking with you all then. Otherwise, stay healthy and keep learning.

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